When manufacturing of patterned magnetic recording media (e.g., bit patterned media (BPM) or discrete track media (DTM)), an ion implantation process may be utilized to transfer the pattern of a patterned resist layer to a magnetic layer of the magnetic recording media. Usually, during such implantation process, a hard mask is disposed over the magnetic layer to allow ion penetration at certain areas of the media's magnetic layer (also known as ion implanted regions) while preventing ion penetration at others (also known as non-ion implanted regions). Those areas of the exposed to the ions are known to exhibit suppressed or substantially reduced magnetic moment in comparison to those areas protected from ions penetration; this difference in magnetic moment result in the pattern magnetic layer.
Typically, for a hard mask to be effective during ion implantation, it must be: (1) capable of stopping the ions from reaching the magnetic layer of the media (which is usually dictated by material composition, density, and mask thickness); (2) extendible to high density or small feature sizes for patterned magnetic recording media (e.g., for BPM, which require a high aspect ratio mask to maintain a thick mask for protection); (3) robust enough to withstand the etching effects of the ion implantation process such that the hard mask is not substantially removed or altered during the ion implantation process; and (4) removable such that after the ion implantation process it can easily removed without damaging the magnetic layer in the process.
Unfortunately, no single conventional masking configuration meets all of these requirements. For instance, when patterning a magnetic layer using ion implantation with nano-imprint lithography (NIL), the resist material used easily etches away during ion implantation, thereby resulting in less sharp transitions in the magnetic layer between areas of the magnetic layer exposed to ions (i.e., ion implanted regions) and areas not exposed to ions (i.e., non-implanted regions). In another example, when a single metal hard mask comprising Ta is used in conjunction with ion implantation, the aspect ratio is usually not extendible to small features, due to the patterned resist thickness decreasing as feature size decreases while the relative etch rates of the resist and Ta are constant. Furthermore, for single metal hard masks that comprise Ta usually can not be removed from the magnetic media without damaging the underlying magnetic layer (the fluorine-based dry etch chemistries required for removal damage the magnetic layer).